1. Field of the Invention
The present invention relates to a zoom lens (a zoom lens barrel), and more specifically to a cam mechanism of a zoom lens for driving at least one lens group guided along an optical axis thereof in a predetermined manner, without rotating about the optical axis.
2. Description of the Related Art
In a zoom lens, a mechanism which guides at least one lens group in the direction of the optical axis (i.e., the optical axis direction) thereof and at the same time drives the lens group in the optical axis direction in a predetermined manner in accordance with the cam track is known in the art. In such a type of mechanism, a mechanism which is provided with a linear guide barrel guided in the optical axis direction without rotating about the optical axis, a cam barrel fitted on the linear guide barrel to be rotatable about the optical axis relative to the linear guide barrel and to be movable in the optical axis direction together with the linear guide barrel, and one or more lens frames positioned inside the linear guide barrel to be associated with the linear guide barrel and the cam barrel, is known in the art. In this mechanism, the linear guide barrel is provided with linear guide projections which extend radially outwards and linear guide slots which extend parallel to the optical axis, the cam barrel is provided on an inner peripheral surface thereof with cam grooves, and each lens frame is provided with guide projections which are respectively engaged in the linear guide slots of the linear guide barrel, and cam followers which are engaged in the cam grooves of the cam barrel so that each of the cam followers can follow the contour (profile) of the corresponding cam groove.
Such a conventional mechanism is designed without consideration of the positional relationship between the linear guide projections and linear guide grooves of the linear guide barrel and/or between the guide projections and the cam followers of each lens frame. This makes it difficult to make the zoom lens small and compact, especially with respect to the diameter of the zoom lens.
The present invention has been made in view of the fact noted above, and accordingly, an object of the present invention is to provide a cam mechanism of a zoom lens that is provided with a linear guide barrel and a cam barrel and that makes it possible to downsize the zoom lens.
To achieve the object mentioned above, according to an aspect of the present invention, a cam mechanism for driving at least one lens group guided along an optical axis thereof without rotating, the cam mechanism including a linear guide barrel which is moveable in a direction of the optical axis without being rotatable about the optical axis, the linear guide barrel being provided with a linear guide projection at one end thereof which extends radially outwards; a cam barrel fitted on the linear guide barrel to be rotatable relative to the linear guide barrel and to be movable in the direction of the optical axis together with the linear guide barrel, the cam barrel being provided with a cam groove on an inner surface thereof; a linear guide slot formed on the linear guide barrel extending parallel to the optical axis; at least one lens frame positioned inside the linear guide barrel; a projection formed on the lens frame to be slidably engaged in the linear guide slot; and a cam follower formed on the projection to be engaged in the cam groove. The linear guide projection and the linear guide slot are formed on the linear guide barrel at the same circumferential position of the linear guide barrel.
Preferably, the linear guide barrel includes an outer flange formed at the one end of the linear guide barrel to define a position of the cam barrel in the direction of the optical axis relative to the linear guide barrel; and the linear guide projection is formed on the outer flange to extend radially outwards from the outer flange. The linear guide barrel further includes an insertion groove formed on the outer flange on a radially inward side thereof to be positioned at the same circumferential position as the linear guide projection in a circumferential direction of the linear guide barrel so that the cam follower, together with the projection, can be inserted into the linear guide slot via the insertion groove.
In an embodiment, a maximum radius of the linear guide barrel, excluding the linear guide projection, is substantially equal to or smaller than a distance from the optical axis to the tip of the cam follower.
In an embodiment, the linear guide projection includes a plurality of linear guide projections which are formed on the linear guide barrel at 120xc2x0 intervals; the linear guide slot includes a plurality of linear guide slots which are formed on the linear guide barrel at 120xc2x0 intervals; the insertion groove includes a plurality of insertion grooves which are formed on the linear guide barrel at 120xc2x0 intervals; and the cam follower includes a plurality of cam followers which are formed on the at least one lens frame at 120xc2x0 intervals.
Preferably, the cam mechanism is incorporated in a zoom lens.
In an embodiment, the zoom lens includes a stationary barrel having a linear guide groove formed on an inner periphery of the stationary barrel, and the linear guide projection is engaged in the linear guide groove of the stationary barrel.
In an embodiment, the zoom lens is incorporated in a digital camera.
According to an aspect of the present invention, a zoom lens is provided, including first and second lens groups which are moved with respect to each other to change a focal length of the zoom lens; a linear guide barrel guided in a direction of an optical axis without rotating about the optical axis, the linear guide barrel having linear guide slots which extend parallel to the optical axis and linear guide projections at one end of the linear guide barrel to extend radially outwards; a cam barrel fitted on the linear guide barrel to be immovable in the direction of the optical axis relative to the linear guide barrel and to be rotatable about the optical axis relative to the linear guide barrel, the cam barrel having first cam grooves and second cam grooves which are formed on an inner peripheral surface of the cam barrel; a first lens frame which holds the first lens group and includes first cam followers which are respectively engaged in the first cam grooves, and first guide projections which are respectively engaged in the linear guide slots; and a second lens frame which holds the second lens group and includes second cam followers which are respectively engaged in the second cam grooves, and second guide projections which are respectively engaged in the linear guide slots. The first lens frame and the second lens frame are moved in the direction of the optical axis by rotation of the cam barrel in accordance with the profiles of the first cam grooves and the second cam grooves, respectively. The linear guide projections and the linear guide slots are formed on the linear guide barrel at the same circumferential positions in a circumferential direction of the linear guide barrel, respectively.
According to another aspect of the present invention, a cam mechanism is provided for driving at least one lens group guided along an optical axis thereof in a predetermined manner, without rotating about the optical axis, the cam mechanism including a linear guide barrel which is moveable in a direction of the optical axis without being rotatable about the optical axis; a plurality of linear guide projections formed on the linear guide barrel at one end thereof extending radially outwards; a cam barrel fitted on the linear guide barrel to be rotatable about the optical axis relative to the linear guide barrel and to be movable in the direction of the optical axis together with the linear guide barrel; a plurality of cam grooves formed on an inner surface of the cam barrel; a plurality of linear guide slots formed on the linear guide barrel extending parallel to the optical axis; at least one lens frame positioned inside the linear guide barrel; a plurality of projections formed on each of the at least one lens frame to be slidably engaged in the plurality of linear guide slots, respectively; and a plurality of cam followers formed on the plurality of projections to be engaged in the plurality of cam grooves, respectively. The plurality of linear guide projections and the plurality of linear guide slots are formed on the linear guide barrel at the same circumferential positions of the linear guide barrel, respectively.
The present disclosure relates to subject matter contained in Japanese Patent Applications No.2000-24038 (filed on Feb. 1, 2000) which is expressly incorporated herein by reference in its entirety.